In a belated recognition of Earth Day earlier this week, I want to write a crash course guide to an issue that is just starting to get coverage in media, but hasn’t really trickled through to the mainstream: the way climate change will impact international security.

Climate Change and Migration

One of the big, obvious threats that has been reported about climate change is rising sea levels, which are set to render many coastal areas that are currently densely populated unlivable. But even articles discussing that problem don’t always get into the ramifications: mass migration and climate refugees. That kind of migration both presents challenges in keeping the refugees safe and for host cities and countries concerned about admitting criminals or extremists.

A major trend around the world is the increasing urbanization of populations: more and more people are moving from the countryside to the cities in search of economic opportunity. This will lead to the creation more megacities, cities with a population of over 10 million. Critical infrastructure in these cities can be overwhelmed by the speed of this population growth. That, combined with the fact that many of the migrants coming to the city are from lower socio-economic classes, means that a lot of that population growth can end up taking the form of slums that lack basic sanitation and infrastructure, and where sometimes municipal law enforcement actually fears to go.

The resulting security vacuum provides an opportunity for criminal groups to seize control of these slums, while the continuous legitimate and illegitimate flows of people and goods in and out of these cities (trade and smuggling, for example,) can provide cover for militants seeking to launch a violent attack in the city. A prime example of this is the 2008 terrorist attacks in Mumbai, where militants from the Pakistani group Lashkar-e-Taiba traveled from Karachi to the waters off the shore of Mumbai with trading ships, then snuck ashore in the slums, where many people saw them, but assumed they were smugglers. Since smuggling is a common occurrence there, and law enforcement rarely enters the slums anyway, no one bothered reporting the militants coming ashore.

Urbanization also presents greater challenges to humanitarian responses to natural or man-made disasters, while densely populated areas and overwhelmed infrastructure makes it easier for diseases to spread more quickly.

Food Security and Revolutions

Another issue you may have read about is food security: the problem of how to feed the growing global population. Scientists predict that the world’s population will hit 9 billion by 2050, and to keep up with the combination of population growth and increasing demand for meat and dairy products as middle classes around the world (hopefully) expand, we will need to double food production.

How does this impact some of the more traditional issues discussed in security studies? Well, for one thing, revolutions around the world, from the French Revolution to the Arab Spring uprisings, were preceded by food shortages and huge increases in the price of staple food items. That is obviously not to say that the food shortages were the only causes of those uprisings, but it does highlight the way that food insecurity contributes to a greater societal instability.

In general, climate change worsens poverty and inequality and increases the effect of economic shocks. It is hard to predict exactly how the consequences of that will play out, but it will not be good for political stability.

At the extreme end of the threats posed by food insecurity, of course, is the potential for wars over access to food and water. Although that fear may sound overblown, the head of the World Bank says “fights over water and food are going to be the most significant direct impacts of climate change in the next five to 10 years. There’s just no question about it.”

I just watched the first episode of the documentary series Years of Living Dangerously examining climate change’s effects around the world. Part of the episode addresses how a multi-year drought played into the start of the Syrian civil war. As one rebel commander put it: “This is a revolution of freedom. And a revolution of the hungry.”